Since Internet is popular in recent years, individuals and enterprises have the demand for the network significantly. The substantial lines of the Local Area Network (LAN) are needed not only to construct at a time, but also to increase the construction cost and decrease the efficiency of construction. Moreover, the temporary demand of network cannot be satisfied. The appearance of WLAN can decrease the construction cost, expand the signal range of Intranet and satisfy the demand of connection to the network on the go.
However, the acceptance and transmission of the WLAN signal are processed through the WLAN AP/router or the antenna of the wireless network card of the laptop computer. At present, monopole antennas, dipole antennas, chip antennas, or helical antennas can be utilized in these wireless network products. The covering ranges of these kinds of antenna patterns are about 360 degrees. From the viewpoint of application, the advantage lies in that more users can use Internet through the AP/router or the wireless network card. However, since the antenna gain is not high, the wireless communication distance is limited. In order to increase the antenna gain, directional antennas can be utilized to increase the transmitting distance.
The most current smart antennas select the desired antenna direction to proceed the communicating transmission by several directional antennas through turning on/off the diode switch from the software. The advantages of these directional smart antennas lie in that (1) the antenna pattern is switched automatically according to users' area, (2) high antenna gain is obtained, and (3) the antenna pattern is controlled by the software. However, the utility rate of this antenna pattern is not high, and only one signal direction is switched. One antenna only has one directional pattern.
Another smart antenna utilizes the single pole double throw (SPDT) diode of Yagi antenna to switch a capacitance to the ground or an inductance to the ground, and the conductor plays the role on the director or the reflector so as to change the antenna pattern. The advantages of using the capacitance or the inductance lie in that the operation will be more convenient than using equivalent capacitance or equivalent inductance, and the conductor is easily replaced while in the low frequency. However, the drawback lies in that the selected capacitance or inductance will become too small to be used if the higher frequency is operated. This is because the capacitance value and the inductance value are too small for manufacturing the element, or because the self-resonant frequency is too low to be used. In other words, the method of switching the capacitance or the inductance is limited in the frequency. The SPDT diode needs two kinds of voltages for selection, and has more complicated circuit design and higher cost. In addition, the insertion loss of the SPDT diode is larger than that of the pin diode, and the antenna gain of the SPDT diode becomes smaller.
It is therefore attempted by the applicant to deal with the above situation encountered in the prior art.